Severe weather in the form of 1 weak tornado, large hail, and damaging thunderstorm downburst winds affected parts of south-central and southeast Wisconsin on Wednesday, June 8, 2011.

The severe weather was related to a vigorous cold front which swept through southern Wisconsin during the mid-afternoon and evening hours Wednesday. Very warm, moist air ahead of the front clashed with drier, cooler air feeding in from the north behind the front. This clash of air masses produced strong thunderstorms over southern Wisconsin. Some of the thunderstorms became severe, producing large hail and damaging straight-line winds.

The weak tornado, rated EF1, spun up in central Dane county, as verified by a National Weather Service damage survey crew on Thursday, June 9th. Assistance with the survey was provided by members of the MidWest Severe Storm Tracking/Response Center. The tornado spun up about 2.5 miles west-southwest of Verona around 741 pm CDT and continued for approximately 21 minutes. It dissipated around 802 pm CDT about 3 miles northeast of McFarland.

Damage consisted primarily of uprooted trees and broken tree branches which fell on power-lines. In Verona, damaged trees or tree branches crushed a garage, and damaged at least one home and a vehicle. Scattered power-outages were noted. Some minor roof shingle damage was seen. The tornado had a maximum width of 100 yards. The path length was about 17.6 miles. This tornado was rated at the bottom of the EF1 category with wind speeds of about 86 to 90 mph. Damage along the path was sporadic. There have been no reports of injuries or fatalities with the severe weather on Wednesday.

Below is the visible satellite image taken at 310 pm CDT, just before thunderstorm initiation in southwest Wisconsin. Click on image for larger version.

Click on the thumbnail image below for an animation loop of the visible satellite imagery from 310 pm through 8 pm CDT. Watch the strong thunderstorms develop over southern Wisconsin extending into Iowa. Look for the pronounced overshooting tops on the thunderstorms, which are indicative of strong upward rising air and severe thunderstorms.

Below is a plot of the tornado path in central Dane County: Click on image for larger version.

Here are pictures of damage seen in the city of Verona. The first eight pictures were taken by Gary Cannalte, Chief Meteorologist at WISC TV-3 in Madison. The last two pictures were taken by Dale Bernstein, President of MidWest SSTRC. Click on images for larger version.

Below are radar reflectivity and storm-relative velocity loops showing the thunderstorms moving through the Madison area that produced the tornado in Verona. Click on images for larger version.

Strong thunderstorms also produced damaging straight-line winds up to 80 mph across portions of South Central into Southeast Wisconsin. Below are radar reflectivity and base velocity images showing this damaging wind event. Click on images for larger version

Below are graphics illustrating the severe weather events reported to the National Weather Service office in Sullivan on Wednesday. The map on the left shows what was reported prior to 7 pm CDT, and the map on the right shows what was reported after 7 pm CDT. Click on images for larger versions.